Tubular element with fins



Oct. 11, 1966 E. MAiLLET 3,277,960

TUBULAR ELEMENT WITH FINS Filed May 11, 1965 2 Sheets-Sheet 1 INVENTOR EN/VEMOIYD MA lLLET BY %m ATTORNEYS Oct. 11, 1966 E. MAILLET 3,2 77,960

TUBULAR ELEMENT WITH FINS Filed May 11, 1965 2 Sheets-Sheet 2 INVENTOR E/Y/VEMO/VO Mfl/LL ET ATTORNEYS United States Patent 3,277,960 TUBULAR ELEMENT WITH FINS Ennemond Maillet, Paris, France, assignor to Commissariat a lEnergie Atomique, Paris, France Filed May 11, 1965, Ser. No. 466,491 Claims priority, application France, Jan. 25, 1962,

885,980, Patent 1,320,186 14 Claims. (Cl. 165--181) This application is a continuation-in-part of patent application Serial Number 252,833, filed January 21, 1963 and a continuation-in-part of patent application Serial Number 252,834, filed January 2-1, 1963, now abandoned.

The present invention relates to tubular elements or heat exchanger walls, and especially to those which are provided with extension or fins for the purpose of increasing the heat transfer surface area and activating convection whether natural or forced. The invention applies more particularly to the case of the cylindrical metallic cans which surround the fuel slugs employed in nuclear reactors, in which the removal of heat evolved as a result of the fission process is carried out by the circulation of a fluid which is in contact with the cans. Among these latter, the invention is even more especially concerned with cans of the type in which the external surfaces thereof are provided with fins which are formed at relatively small distances apart and which are oriented at an oblique angle with respect to the general direction of flow of the fluid, the said fins being arranged in an even number of series or sectors around the body of the can, the fins in two adjacent sectors being inclined in opposite directions in such manner as to recall the pattern of gears of the so-called herringbone type.

It is known that the arrangement of fins of this type in a herringbone pattern gives rise to controlled eddy currents at the center of the fluid flow, thereby producing the separation of this latter into distinct spiral streams which follow the different peripheral sectors of the can. Since the fins are set perpendicularly in each of the sectors and have sides or walls next to helicoidal surfaces which are coaxial with the can, the profiles of the unitary grooves or channels which are formed between successive fins consequently provide a rather poor connection with the spiral eddy currents which are induced by the fins and the axes of which are parallel to that of the can but located outside the perimeter thereof. The fins thus form screens which make the path of the fluid subject to abrupt deviations which increase pressure losses and slow down the convection currents.

Accordingly, the present invention has among its objects to provide a remedy for this drawback by permitting of a more effective renewal of the fluid in the unitary channels which are formed between two successive fins, a more uniform temperature distribution throughout all the sections of the can, a reduction of flow resistance and a lesser tendency to deformation in spite of the effects of radiation and the various thermal and aero-dynamic stresses which are created.

To this end, a tubular element with cooling fins arranged in adjacent sectors forming herringbone configurations is characterized in that the fins are of constant height over a major portion of their length and substantially 3,277,960 Patented Oct. 11, 1966 parallel to each other in each sector. The fins on the element may be planar or helicoidal.

Apart from this principal arrangement, a tubular element in accordance with the invention is characterized by other relative arrangements to be considered either separately or in combination and which concern especially the profile imparted to the bases of the unitary grooves or channels between fins, that is to say the shape of the external wall of the element, as well as the external configuration of the said fins, in particular at the extremities thereof at the limits of each sector.

One modification of the invention mainly consists in supporting each of the fin sectors on a portion of the external wall of the tubular element which is delimited by two generator lines, each of the said portions having a cylindrical surface having its axis parallel to the axis of the element and the cross-section of which, taken along a plane at right angles to the said axis, has a general concavity which is directed towards the exterior of the said element. In another modification, the external surface of each of the portions is planar.

Apart from the above, the invention also consists in various other arrangements by means of which it is possible on the one hand to arrange in contact with the fin sectors spiral streams of circular outline which are located next to stable streams flowing in vortical motion and which ofifer the minimum energy losses and, on the other hand, to reduce the mechanical stresses and heat concentrations which are liable to result in creep of the material constituting the tubular element and the fins by means of an appropriate adaptation of the shapes and dimensions of the said fins as well as the ribs or notched portions which separate two adjacent sectors.

The invention further consists in various other arrangements which will be explained in greater detail below in the course of the description of a number of examples of construction which are given by way of indication and not in any sense by way of limitation.

In the accompanying drawings:

FIGURE 1 is a view in perspective of one form of embodiment of the invention;

FIGURE 2 is a view in cross-section of another form of embodiment which constitutes an extreme case of FIG- URE 1;

FIGURE 3 is a view taken in perspective of another form of embodiment of the invention; and

FIGURE 4 is a view in cross-section of another form of embodiment which constitutes a generaliaztion of the case considered in FIGURE 3.

There can be seen in FIGURE 1 a tubular heat transfer element 1 or member, the central portion 2 of which is reserved for the circulation of a primary fluid in the case of a heat exchanger tube, or for the fitting therein of a slug of fissile material in the case of a nuclear fuel can.

In the example considered, the external surface of the tubular element 1 is divided into six identical sectors which are respectively designated by the references 3a, 3b, 30, etc., each sector being delimited by two generator lines such as the generator lines 4 which are parallel to the axis of the element 1. In each of the said sectors, the element is provided with several series of helicoidal fins 5 which are set perpendicularly on the corresponding surface and form between two successive parallel fins unitary grooves or channels for the circulation of a cooling fluid which lflows outside the fins 5 with a general direction of flow which is shown in diagrammatic manner by the arrow 6. The fins 5, which are of constant height over the major portion of the entire length thereof, are distributed from one sector to the adjacent sector in series which are alternately inclined in opposite directions in such manner as to form longitudinal herringbone patterns, the effect thereof being to induce in the flow in known manner a 'vortical motion of spiral pattern which periodically brings back the fluid in contact with the fins into the interior of the unitary channels formed between these latter.

Accordingly, in order that the circulation of the fluid should be facilitated in accordance with the invention, each of the sectors 3a, 3b, 30, etc. has a cylindrical surface, 9a, 9b, 90, etc., the axis of which is parallel to that of the element 1 but located outside the perimeter of this latter. The body of the tubular element thus has in right crosssection the shape of a curvilineal polygon whether regular or not.

The concavity of the unitary channels or grooves between the fins in each of the sectors is directed outwards with respect to the axis of the element, thereby very substantially reducing the resistance offered to the flow of fluid and at the same time increasing the COCfl'lClBIlt of heat transfer. In addition, the curvature of the mean concavity must be increased with the number of sectors for a given size of can in order to obtain a stable flow.

FIGURE 2 represents a view in cross-section taken in a plane at right angles to the axis, of a tubular heat transfer element or member 11 which is shown as an extreme case of the general arrangement of FIGURE 1. In fact, it will be noted in this particular form of embodiment that the exterior surface 19a, 19b, 190, etc., of the sectors 13a, 13b, 130, etc., have a rectilineal and no longer concave outline which corresponds to an infinite radius of curvature or at least a very large radius with respect to the diameter of the element. Each of the sectors 13a, 13b, 130, etc., is defined by two generator lines 14 which are parallel to the axis of the element 11. The fins 15 of constant height are again helicoidal and set perpendicularly to the can but can comprise all the secondary modifications which have been explained in detail in the foregoing, with a view to facilitating the penetration or ejection of the small streams of fluid. It can be observed in addition that the tubular element or can 11 is provided with lateral extensions such as the extensions 8 which are formed in one piece with the said element and are intended to effect the centering of this latter inside a channel or, more usually, inside the annular space through which the coolant circulates. These centering members can have any appropriate shape and are provided in particular with recesses or hollowed-out portions, not shown, the dimensions of which must be compatible with their mechanical strength under the conditions of use.

There has been illustrated in FIGURE 3 a tubular heat transfer element or member 31, the central portion 32 of which is reserved for the circulation of a primary fluid in the case of a heat-exchanger tube, or for the fitting therein of a slug of fissile material in the case of a nuclear fuel can.

In the example considered, the external surface of the tubular element 31 is divided into six identical sectors which are respectively designated by the references 33a, 33b, 330, etc., each sector being delimited by two generator lines such as the generator lines 34 which are parallel to the axis of the element 31. In transverse cross-section, the body of the element accordingly has the shape of a polygon whether regular or not. In each of the sectors, the element is provided in accordane with the invention with several series of a planar and parallel fins such as the fins 35 which are set preferably perpendicularly on the corresponding surface of the element, or which can if necessary be set at an oblique angle, and which form between two successive fins unitary grooves or channels for the circulation of a cooling fluid which flows outside the fins 35 with a general direction of flow which has been shown in diagrammatic manner by the arrow 36. The fins 35, which are of constant height over the major portion of the entire length thereof, are distributed from one sector to the adjacent sector in series which are alternatively inclined in opposite directions in such manner as to form herringbone patterns, the effect thereof being to induce in the flow in known manner vortical movements or eddy currents of substantially spiral motion which periodically bring back the fluid in contact with the fins into the interior of the unitary channels formed between these latter.

In order to facilitate the circulation of the fluid and in order to facilitate at the same time the machining of the fins on the body of the element, each of the sectors 33a, 33b, 330, etc., has a plane surface 39a, 39b, 390, etc., which imparts to the transverse cross-section of the element in the case considered in FIGURE 3 the shape of a regular hexagon. The unitary channels between the fins in each of the sectors thus have a substantially rectangular profile, the width of the channels being designed to reduce to a very appreciable extent the resistance offered to the flow of fluid and at the same time to increase the coelficient of heat transfer.

It is wholly apparent, in all cases however, that other complementary arrangements can be employed at the same time in order to facilitate either separately or simultaneously the admission of the small streams of fluid in the interior of the channels between the fins and the return of the said small streams to the main current of fluid. Accordingly, in order to accelerate the renewal of the fluid, the angle at which the fins are inclined with respect to the axis of the element can be chosen within the limits of 10 to 70 with an optimum comprised between 15 and 45. Similarly, the number of series of fins and consequently of surfaces of the element can be variable. In particular, in the case in which the tubular element is a can for nuclear fuel located inside the channel of a reactor, it is observed that the said number depends on the ratio of the internal diameter of the can to that of the diameter of the channel. By way of example, and in the case which is more especially considered in FIGURES 1 and 3 the ratio referred to above must be comprised between 0.30 and 0.50. It will thus be noted that the number of series of fins can be reduced to four in the case of an element having a small diameter located inside a channel which has a large transverse dimension, while the said number of series of fins can be increased to ten or twelve in the case of elements having relatively large diameters in a small space, the shape and dimensions of the said fins being suited to each particular case.

In all cases, the height of the fins is substantially con stant over the entire length, the profile of the said fins being rectangular or trapezoidal, this latter case offering the advantage of endowing the fins with better mechanical strength. In addition, provision can be made, in order to facilitate the admission and discharge of the fluid in the unitary channels, to machine and bevel the fins very slightly at their extremities or longitudinal edges so as to form along the generator lines which separate the sectors, recessed portions, the shape of which can be substantiallv triangular or dovetailed.

It is also possible to deform or deflect the ends of the fins to a slight extent, thereby causing the angle of inclination of the said ends to vary with respect to the axis of the can; it is also possible to form at these points, that is to say in fact in the zones of penetration or ejection of the small streams of fluid, chamfers or feather edges of suitable shape; it is also possible to combine these two arrangements.

FIGURE 4 represents a view in cross-section taken in a plane at right angles to the axis, of a tubular element 41 having a hollow central portion 42 and which illustrates a form of embodiment to be considered as a generalization of the case of the element which is represented in FIG- URE 3.

In fact, it will be noted in this particular form of embodiment that the sectors such as 43a, 43b, 43c, etc., have a cylindrical surface 49a, 49b, 49c, etc., the cross-section of which along a plane at right angles to the axis presents a concavity which is directed outwards from the element.

The lateral limit of each of the sectors 43a, 43b, 430, etc., is defined by two generator lines 44, which are parallel to the axis of the member 41. The fins 45 of constant height are again plane and set at right angles to the can but may comprise all the secondary modifications which have been explained in the foregoing, with a view to facilitating the penetration or ejection of the small streams of fluid. As already mentioned above with regard to FIG- URE 3 the tubular element or can 41 is provided with lateral extensions such as the extensions 48 which are formed in one piece with the said element and are intended to effect the centering of this latter inside a channel or, more generally speaking, inside the annular space through which the cooling fluid circulates. These centering members can have any appropriate shape and are provided in particular with recesses or hollowed-out portions not shown which are preferably located in the zones of junction with the wall of the element and the dimensions of which must be compatible with their mechanical strength under the conditions of use.

It will be understood that the invention is not in any sense limited to the forms of embodiment which have been described and illustrated, and which have been given solely by way of example. It accordingly follows that the arrangements of details such as the centering members which form one piece with the tubular element is not limited to the form of embodiment of FIGURES 2 and 4 but can be contemplated in the particular case of FIG- URES 1 and 3.

I claim:

1. A heat transfer element, comprising: a tubular member having a passage extending therethrough, the outer surface of said member being of generally polygonal configuration as viewed in transverse cross-section and providing a plurality of identical sectors arranged therearound, the external surface of each of said sectors being cylindrical with the axes of the cylindrical surfaces extending parallel with the axis of said member and being disposed outwardly from the outer surface of said member so that a projection of the external surface of said sectors onto a plane at right angles to the axis of said member defines for each sector a curve having a general concavity which is directed outwardly from the member; and a plurality of fins formed integral with said member and extending outwardly from the surface of each of said sectors; the fins being parallel to each other on each sector and inclined at an angle to the axis of said member and in opposite directions in adjacent sectors so as to form a herringbone pattern, the fins on each sector defining portions of helicoids and being of constant height over a major portion of their length.

2. A heat transfer element in accordance with claim 1 in which the axes about which the fins are generated are located inside the perimeter of the tubular member and parallel to the axis of the latter.

3. A heat transfer element in accordance with claim 1 in which the axes about which the fins are generated are located outisde the perimeter of the tubular member and parallel to the axis of the latter.

4. A heat transfer element, comprising: a tubular member having a passage extending therethrough, the outer surface of said member being of generally polygonal configuration as viewed in transverse cross-section and providing a plurality of identical sectors arranged therearound, the external surface of each of said sectors being cylindnical with the axes of the cylindrical surfaces extending parallel with the axis of said member and being disposed outwardly from the outer surface of said member so that a projection of the external surface of said sectors onto a plane at right angles to the axis of said member defines for each sector a curve having a general concavity which is directed outwardly from the member; and a plurality of fins formed integral with said member and extending outwardly from the surface of each of said sectors; the fins being parallel to each other on each sector and inclined at an angle to the axis of said member and in opposite directions in adjacent sectors so as to form a herringbone pattern, the fins on each sector being of substantially constant height over a major portion of their length.

5. A heat transfer element in accordance with claim 4 in which the herringbone series formed by the fins in at least two adjacent sectors are separated from adjacent herringbone series by lateral extensions of the wall of the member.

6. A heat transfer element in accordance with claim 5 in which the lateral extensions are provided on one side only of each sector.

7. A heat transfer element in accordance with claim 4 in which the extremities of each fin at the longitudinal edges of each sector are beveled so as to form, along the generator line of separation between two adjacent sectors, notches of generally triangular shape.

8. A heat transfer element in accordance with claim 4 in which the fins on each said sectors extend outwardly perpendicular to the surface thereof.

9. A heat transfer element in accordance with claim 4 in which the fins on each of said sectors extend outwardly at an oblique angle to the surface thereof.

10. A heat transfer element, comprising: -a tubular member having a passage extending therethrough; the outer surface of said member being of generally polygonal configuration as viewed in transverse cross-section and providing a plurality of identical sectors arranged therearound; the surfaces of the sectors which are located between two consecutive fins in a same sector being formed so that a projection thereof onto a plane at right angles to the axis of said member defines a curve having a general concavity which is directed outwards from the member; and a plurality of fins formed integral with said member and extending outwarly from the surface of each of said sectors, the direction of the said fins on each sector being inclined at an angle to the axis of said member and opposite to the direction of the fins on the adjacent sectors so as to form herringbone series, the fins being planar and substantially parallel to each other in each sector and being of constant height over a major portion of their length.

11. A heat transfer element, comprising: a tubular member having a passage extending therethrough, the outer surface of said member being generally polygonal configuration as viewed in transverse cross-section and providing a plurality of identical sectors arranged therearound and with the external surface of each of said sectors being planar, and a plurality of fins formed integral with said member and extending outwardly from the surface of each of said sectors; the fins being parallel to each other on each sector and inclined at an angle to the axis of said member and in opposite directions in adjacent sectors so as to form a herringbone pattern, the fins on each sector being of substantially constant height over a major portion of their length.

12. A heat transfer element comprising: a tubular member having a passage extending therethrough, the outer surface of said member being of generally polygonal configuration as viewed in transverse cross-section and providing a plurality of identical sectors arranged therearound, and a plurality of fins formed integral with said member and extending outwardly from the surface of each of said sectors; the fins being parallel to each other on each sector and inclined at an angle to the axis of said 7 member and in opposite directions in adjacent sectors so as to form a herringbone pattern, the fins on each sector being of substantially constant height over a major portion of their length.

I13. A heat transfer element, comprising: a tubular member having a passage extending therethrough, the outer surface of said member being of generally polygonal configuration as viewed in transverse cross-section and providing a plurality of identical sectors arranged therearound, land a plurality of fins formed integral with said member and extending outwardly from the surface of each of said sectors; the fins being parallel to each other on each sector and inclined at an angle to the axis of said member and in opposite directions in adjacent sectors so as to form a herringbone pattern, the fins on each sector defining portions of heliooids and being of substantially constant height over a major portion of their length.

8 14. A heat transfer element, comprising: a tubular member having a passage extending therethrough, the outer surface of said member being of generally polygonal configuration as viewed in transverse cross-section and providing a plurality of identical sectors arranged therearound, and a plurality of fins formed integral with said member and extending outwardly from the surface of each of said sectors; the fins being parallel to each other on each sector and inclined at an angle to the axis of said member and in opposite directions in adjacent sectors so as to form a herringbone pattern, the fins on each sector being planar and of substantially constant height over a major portion of their length.

No references cited.

FREDERICK L. MATTESON, ]R., Primary Examiner. 

1. A HEAT TRANSFER ELEMENT, COMPRISING: A TUBULAR MEMBER HAVING A PASSAGE EXTENDING THERETHROUGH, THE OUTER SURFACE OF SAID MEMBER BEING OF GENERALLY POLYGONAL CONFIGURATION AS VIEWED IN TRANSVERSE CROSS-SECTION AND PROVIDING A PLURALITY OF IDENTICAL SECTORS ARRANGED THEREAROUND, THE EXTERNAL SURFACE OF EACH OF SAID SECTORS BEING CYLINDRICAL WITH THE AXES OF THE CYLINDRICAL SURFACES EXTENDING PARALLEL WITH THE AXIS OF SAID MEMBER AND BEING DISPOSED OUTWARDLY FROM THE OUTER SURFACE OF SAID MEMBER SO THAT A PROJECTION OF THE EXTERNAL SURFACE OF SAID SECTORS ONTO A PLANE AT RIGHT ANGLES TO THE AXIS OF SAID MEMBER 